1. Field of the Invention
The present invention relates to an anode for the electrolysis of water, which has high durability and low oxygen overvoltage. More particularly, the present invention relates to an anode which hardly undergoes degradation of its properties even when subjected to an oxidizing environment and which has a low oxygen overvoltage characteristic.
2. Description of the Prior Art
Various types of anodes have been proposed as anodes having low oxygen overvoltage, particularly as anodes for electrolysis of water in an aqueous alkaline solution.
As an industrial process for the production of oxygen and hydrogen, it is well known to obtain oxygen gas from an anode compartment and hydrogen gas from a cathode compartment in the electrolysis of water in an aqueous alkaline solution in an electrolytic cell. As an anode for such an electrolytic cell, it is preferred to use iron, nickel or Raney nickel.
However, the oxygen overvoltage of such an anode is not low enough. In the case of nickel or cobalt, the overvoltage tends to increase as time passes. The present inventors have studied this phenomenon, and finally found that the nickel or cobalt surface as an electrochemically active component is converted to nickel hydroxide or cobalt hydroxide, whereby the electrochemical activity is deteriorated, i.e. the oxygen overvoltage increases. Further, it has been found that this deterioration can effectively be prevented by incorporating a third component selected from the group consisting of a noble metal and rhenium into known metal particles comprising a first component such as nickel or cobalt and a second component such as aluminum, zinc, magnesium or silicon, and that not only such metal particles but also an electrode having a surface layer having the same composition is equally effective. The present invention has been accomplished based on these discoveries.